Simplomys meulenorum, García-Paredes & Peláez-Campomanes & Álvarez-Sierra, 2009

García-Paredes, Israel, Peláez-Campomanes, Pablo & Álvarez-Sierra, M. Ángeles, 2009, Gliridae (Rodentia, Mammalia) with a simple dental pattern: a new genus and new species from the European Early and Middle Miocene, Zoological Journal of the Linnean Society 157 (3), pp. 622-652 : 644-645

REMARKS ON SIMPLOMYS MEULENORUM SP. NOV.

In the localities of the Aragonian type area, S. meulenorum sp. nov. does not show much morphological variation but does show morphological simplification of the m3. In the older localities of zone B, the m3 is already quite reduced and most specimens develop a single posterior ridge and full reduction of the posterior valley. In localities from the middle part of zone B until the end of zone C, only this completely reduced morphology is found.

Ongoing research shows the presence of this species in the Ramblian. These assemblages will allow us to get a better understanding of the primitive character state of the m3.

The m3 of S. meulenorum sp. nov. and S. simplicidens have the mesolophid and posterolophid fused into a single ridge, but this union is achieved in different ways in both species. In S. meulenorum sp. nov. the mesolophid is almost completely reduced so the last ridge is mainly composed of the posterolophid ( Fig. 8L, P ). In S. simplicidens the labial part of the mesolophid and the lingual part of the posterolophid are short as is shown in specimens with intermediate simplification; thus, the last ridge is equally composed of the lingual part of the mesolophid and the labial part of the posterolophid separated by an inflexion ( Fig. 4H ). This inflexion is interpreted as a narrow trace of the posterior valley and is situated medially, whereas in S. meulenorum sp. nov. it is near the lingual border. Other morphological differences between the m3 of these species have been observed. In S. meulenorum sp. nov. the central valley is deeper than in S. simplicidens . In S. meulenorum sp. nov. the posterior part is lower than the anterior one and the posterior wall of the ridges is more inclined than in S. simplicidens .

In the P4 of Simplomys meulenorum sp. nov. the main cusps are less distinguishable than in S. simplicidens .

An unusual morphological feature in Gliridae is found in S. meulenorum sp. nov. In the M1, the anteroloph may be interrupted and connected medially to the protoloph ( Fig. 8B, F ). The taxonomical or functional value of this particular morphology is not clear, but it is present in half of the M1 of S. meulenorum sp. nov. from all localities, whereas it is much less common in the M1 of S. simplicidens .

Simplomys meulenorum sp. nov. and S. simplicidens show statistically significant differences in length, width, and surface for all dental elements when these two species occur in the same locality (Table 4); S. meulenorum sp. nov. is the larger one.

Simplomys meulenorum sp. nov. shows a trend to size increase through time in the studied area ( García-Paredes, 2006) ( Fig. 10 ). As a result of this trend, size ranges of S. meulenorum sp. nov. may overlap with S. robustus . However, different morphologies allow us to distinguish them.

The material originally described as Pseudodryomys robustus from the Spanish locality Córcoles (zone C, Tagus basin) ( Díaz Molina & López Martínez, 1979; Alférez et al., 1982; Álvarez Sierra et al., 1994; Alférez et al., 1999; Morales et al., 1999) has been revised and is assigned to S. meulenorum sp. nov.

Figures

Figure 4. Simplomys simplicidens (De Bruijn, 1966) from Valdemoros 3F (Fig. 4A–H) and Artesilla (Fig. 4I–P) (collection MNCN). A, P4 VA3F-27. B, M1 VA3F-39. C, M2 VA3F-52. D, M3 VA3F-62. E, p4 VA3F-342. F, m1 VA3F-73. G, m2 VA3F-76. H, m3 VA3F-95. I, P4 ART-1134. J, M1 ART-931. K, M2 ART-943. L, M3 ART-1173. M, p4 ART-2455. N, m1 ART-966. O, m2 ART-990. P, m3 ART-1186. Right side specimens underlined.

Figure 8. Simplomys meulenorum sp. nov. from Artesilla (collection MNCN). A, P4 ART-1142. B, M1 ART-874. C, M2 ART-882. D, M3 ART-1164. E, P4 ART-1227. F, M1 ART-873. G, M2 ART-886. H, M3 ART-1163. I, p4 ART-2498. J, m1 ART-901. K, m2 ART-910. L, m3 ART-1156. M, p4 ART-2499. N, m1 ART-894 holotype. O, m2 ART-918. P, m3 ART-1158. Right side specimens underlined. Holotype in italics.

Figure 10. Temporal distribution of average surface of the upper and lower cheek teeth in species of Simplomys gen. nov. from the Aragonian type area (Calatayud–Montalbán basin, Spain). Only localities with at least five measurable specimens of each element are included. Horizontal bars represent two times the standard deviation. Modified after García-Paredes, 2006.